Question

Find an exact value.

cos 15°

Answer 1

setting 15 = (45-30)

Answer 2

then use the formula :
cos(A-B) = cosAcosB + sinAsinB

Answer 3

here given A=45 and B=30 degrees

Answer 4

cos 45cos30 +sin45cos30?

Answer 5

45 and 30 are the special angles.. u have to remember the values of sin and cos for angles 30 and 45 degrees

Answer 6

ok. how do i solve from here?

Answer 7

u just put the values of them (sin45, sin 30, cos45, cos 30)

Answer 8

cos 45cos30 +sin45cos30
= ... (calculate it and simply)

Answer 9

i got this

Answer 10

hmm.. what identity did u use ?
it should be : cos 45cos30 +sin45cos30
do u know the exactly value of sin30 ? sin45 ? cos30 ? cos45 ?

Answer 11

just put the values cos45 =1/root 2 and cos 30= root3/2

Answer 12

sin 45=1/root ovr2 and sin 30=1/2...the multiply and add

Answer 13

1/root ovr2 or 1/ root 2?

Answer 14

its the same thing...

Answer 15

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